Colloidal Silica" - Consolidation injections system and waterproofing of rocks and granular .......

ILLUSTRATIVE TECHNICAL REPORT Consolidation injections system and waterproofing of rocks and granular soils or stone structures with "colloidal silica"

Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

Premise The possibility of injecting a plot, using a mixture able to modify its geotechnical characteristics, remains today one of the most effective techniques for improvement of soils for improving the geotechnical characteristics of soils.

The applicability fields of "colloidal silica" based mixtures depend on numerous external parameters, linked both to the characteristics of the soils to be permeated, and to the injection techniques.

Laboratory tests were mainly focused on the rheological characterization of the mixtures used, on their effective penetration capacity in granular sample soils and on the resistance parameters obtainable on the injected soil.

Our main objective is to illustrate the properties of STONE-CSG for colloidal silica based injection, through the characterization of the mixture and its ability to penetrate into various granular soils.

The laboratory tests carried out have demonstrated the actual capacity of "colloidal silica" in achieving excellent penetration and excellent consolidation in granular soils, even with fine grain percentages.

All photos illustred are copied from the WEB

Colloidal silica The "colloidal silica", which is the basic element of mineral mixtures for injections (such as STONE-CSG), is an aqueous suspension in which microscopic silica particles are dispersed.

Injection pressure is defined as the introduction of a material into a soil or a stone structure (wall structure or concrete) in order to consolidate and waterproof voids, cracks and porosity.

Colloidal silica is an aqueous suspension in which silica particles of infinitesimal dimensions are dispersed which do not tend to settle and with a viscosity comparable to that of water (the gelation time is regulated with an accelerating additive).

It is an environmentally friendly substance that lasts over time, being simply composed of silicon oxide, water and salt. Having the consistency of water (low viscosity), it easily penetrates into very fine sand and micro-fractures, drastically reducing permeability. It has the advantage of not being evolutionary, that is to maintain the viscosity until solidification. The most important aspect of its "non-evolution" is the adjustable time interval with the “Accelerator-CSG-kat "according to the needs.

Figure 1 - Permeability of some injection mixtures according to the characteristics of the porous system

Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

Colloidal silica characteristics - Colloidal silica particles have a variable size from about 4 to 16 nm (nm = 10-9 m = 10-6 mm) and, by virtue of their infinitesimal dimensions, are not affected by gravity and therefore do not tend to settle. The result is a very high blaine, of the order of 200 ÷ 300 m2 /g depending on the type.

- The particles consist of SiO2, that is quartz, and in particular a tetrahedral distribution of atoms that gives it its amorphousness, unlike other crystalline compounds based on SiO2, whose atoms are ordered at the molecular level (crystalline silica) ).

Moreover, the pH is between 9 and 11, while sodium silicates have pH values of 12-13.

These aspects imply that the colloidal silica is in the form of polymers rather than constituted by monomers, aspects that increase their capacity for interaction and stability (durability).

- Colloidal silica has a very low viscosity (5 -10 cP) depending on the type, comparable to that of water which is equal to 1 cP (for comparison, the viscosity of the silicates varies between 80 and 180 cP); this allows the colloidal silica to penetrate in soils with a low K value (10-4 ÷ 10-5 m/s), where the usual technologies do not allow satisfactory results.

- With the addition of the accelerant it is possible to optimally adjust the gel time.

However, both STONE-CSG-200 and STONE-CSG-300 can be considered monocomponent systems, since, although they are made up of colloidal and accelerating silica, they are commonly injected with normal single-component pumps.

- Colloidal silica does not exhibit syneresis phenomena, that is to say, gel shrinkage, due to the separation between solid and liquid parts, which causes water to be expelled, with consequent decay of the injection.

All photos illustred are copied from the WEB

- The formulation STONE-CSG-200 that STONE-CSG-300, based on colloidal silica, are chemically and biologically inert and non-toxic.

Figure 2 - Diagram of gelling time according to the percentage of accelerant (T = 20 ° C)

Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

Laboratory characterization tests of colloidal silica The laboratory method used to measure the gelation time of the colloidal silica with the addition of “Accelerator-CSG-kat” to 10% NaCl was as follows: - mixing of 0.2 l of silica with the accelerator (at different percentages) by means of a colloidal mixer (1800 rpm) for 10 seconds;

All photos illustred are copied from the WEB

- the gelling time measurement starts immediately after mixing and stops when the mixture is no longer able to flow.

The trend over time of the transformation of the silica gel, depending on the percentage of accelerator (NaCl) used is well expressed by the graph of Figure 2.

Figure 3 - Diagram of mechanical strengths in function of time (days)

Action mechanism The surface of the silica is hydrated as SiOH and is negatively charged: consequently the repulsive forces between the particles prevent the collision with each other.

Once the repulsion forces are gradually attenuated by the introduction of the accelerator, the particles begin to collide with each other: thus begins the process of gelling, whereby a real three-dimensional lattice is formed and the aggregation continues until the gelling process is completed (formation of Si-O-Si bonds).

All photos illustred are copied from the WEB

Photo

-

Colloidal Silica Reaction - particle size 0.015 µm - the Colloidal Silica surface is hydrated as SiOH and it is negatively charged: consequently the repulsive forces between the particles prevent the collision with each other.

Once the repulsion forces are gradually attenuated by the introduction of the Accelerant-K2, the particles begin to collide with each other: so begins the gelation process, so it is to form a real three-dimensional network and l ' aggregation continuous until the gelling process is completed (formation of Si-O-Si bonds).

Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

The mechanical properties (mainly resistance and deformability) and hydraulic properties (permeability) of the soil can be improved through the injection of colloidal silica products, with small diameter perforations (very large diameter perforations can also be made 80 cm).

In the recent past the use of cement-based mixtures has been particularly used in soils with high permeability, such as gravels and coarse sands, while in the presence of less permeable soils, such as fine sand and silt, it was necessary to resort to the use of finer suspensions (ultrafine cements) and/or chemical solutions (gels, resins).

Today, however, the choice of the hydrophilic mixture, low viscosity, based on colloidal silica is necessary for its specificity to be used in waterproofing and consolidation injections in inconsistent and rocks in stratified terrains sandy-silt.

One of the fundamental characteristics of this mixture is that which has a gelling time which can be regulated by the addition of an accelerator, or a solution of sodium chloride (NaCl) in water, which acts as an activator of the gelling process.

Colloidal silica particles have a size ranging from about 4 to 16 nm and do not tend to settle in solution.

Fields of use Given the aforementioned characteristics, colloidal silicas such as STONE-CSG-200 and STONE-CSG-300 allow consolidation and/or waterproofing injections to be carried out in stratified sedimentary soils of sand-silty nature and in particular: - pre-consolidation injections for the tunneling, mining and engineering sector in general; - waterproofing interventions in case of transudation or infiltration of water in metropolitan tunnels under construction or existing; - interventions in existing buildings to reduce their failures, to allow renovations or to safeguard against instability due to new or adjacent works (constructions); - sealing and / or consolidation alternatively of sheet piling, diaphragms of various types, lowering of groundwater, etc .; - consolidation of degraded rocky escarpments; - improvement of the geotechnical characteristics of the land; - waterproofing of tunnels and large dams, in particular the construction of diaphragm (waterproof screen) pushed up to the base rock. As also realization of consolidating treatment of dams placed on alluvial soils and rock; - interventions for the protection of large earthworks of alluvial soils below the water table.

Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

All photos illustred are copied from the WEB All photos illustred are copied from the WEB

Photo - Example of consolidation activity of a land carried out by the surface realized by IMPREGILO spa in Monza (Italy) as part of the modernization works of the State Road 36 in relation to the construction of the new "Alto Lambro" sewage collector, a circular underground pipeline with an internal diameter of 250 cm (external 300 cm) and a total length of 2.8 km. The solution used saw the use of "colloidal silica", a material with a great penetrative capacity, in some cases a serious alternative to the more usual cement injection or jettinjection systems.

A non-invasive product because its nanometric size requires low discharge pressure, absolutely inert from the chemical point of view, free from solvents and toxic components, the material returns discrete cohesion rates to the soil matrix, while improving its deformation characteristics.

All photos illustred are copied from the WEB

Photo - Detail of the injection pipes

Photo - left photo of the soil sample after consolidation treated with "silica" while on the right photo of virgin soil (untreated) before consolidation

Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

Choice on the type of formulation to be used The difference between STONE-CSG-200 and STONE-CSG-300, by virtue of the different production process, consists of the larger specific surface area (about 200 - 300 m2/g of the first compared with about 170 m2/g of the second) and in the concentration (15% against 40%).

This difference leads to a greater initial reactivity for STONE-CSG-200 (prevalence of fineness), which can make this formulation more suitable for rapid waterproofing interventions, while the highest concentration of STONE-CSG-300 can be advantageous in time long for a greater degree of gelation.

Incoherent land Before moving on to the next paragraph to illustrate the Injection tests on incoherent soils with "colloidal silica" I want to illustrate some brief notions on the granulometric curves at the limits of penetrability of incoherent soils.

Granulometry From a granulometric curve one can deduce various parameters, more or less significant and correlable with the permeability depending on the case: a)- the composition described below is referred in percentage to conventional granulometric classes: Ø grains d (mm) Pebbles and blocks Gravel Sand Silt Clay with

further

> 60 60 ÷ 2 2 ÷ 0,06 0,06 ÷ 0,002 < 0,002

subdivision

into

large-medium-fine

within

each

class;

b) - the effective diameter d10, corresponding to 10% of fraction lower than d, in the granulometric curve; c) - the degree of non-uniformity U = d60 / d10 being d60 the diameter corresponding to 60% of fraction lower than d; d) - the specific surface of the grains, referable to the volume unit (So in cm-1) or to the weight unit (Ss in cm2 / g = cm2 / cN).

Classification a) already gives us an initial orientation judgment on the possible methods of treatment.

Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

The diameter d10 allows us to qualify the finest fraction (ie more conditioning to the effects of injectability) and can be directly related to the permeability when the material is rather uniform.

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The verification of such a situation, very frequent in alluvial deposits, is very important as it allows to program a differentiated treatment with colloidal silica formulations of penetrability adequate to the individual layers, for thin that they can be.

Fig. 4 - graphic illustration of the different injector materials suitable for different grain sizes

Colloidal Silica Microfin cements Cement injections

Porosity and relative density The porosity (n) expresses the total volume of voids, referred to the unit of soil volume.

Evaluation can be done more or less accurately in various ways: a) - on undisturbed samples, based on the relationship between the dry density ys and the specific gravity of the ysp grains; b) - on samples that are remanent (but granulometrically representative), determining the extreme values nmin and nmax with a normalized procedure and deducing n from empirical correlations between relative density Dr and data of in situ penetrometric tests; c) - indirect methods in situ (electrical, with radioisotope probes, etc.).

Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

The porosity (n) is a global index that increases with the fineness of particle size (ie, with the decrease of the average size of the pores), with the same relative density. For each soil data the porosity qualifies the degree of thickening, influencing to a certain extent the permeability, and is also indicative of the theoretical amount of colloidal silica required for impregnation.

In the field of injectable soils, the porosity is on average between 0.2 and 0.3 for the most coarse and between 0.3 and 0.4 for the finest.

It should be noted that the volume of filled voids does not generally exceed 50% of the total porosity (n). The higher consumption of Colloidal Silica can be attributed to an increase in the initial volume of the voids and to dispersions.

Injection test of incoherent soils with "colloidal silica" The method adopted in the laboratory for the laboratory injection test of colloidal silica to define significant parameters for the purposes of injectability in incoherent soils is illustrated below.

The soil samples must be left to rest in the air at a temperature of 20 ± 2 ° C and will have to reproduce the actual granulometric composition.

The volumetric characteristics (density, porosity) will be evaluated only on samples that give guarantees of good conservation of the original structure.

In the test soil injections the pressures reached are between 2 and 10 bar and no particular difficulties have been found in completely permeating all the available natural materials.

The method adopted for laboratory injection tests was as follows: - preparation of PVC pipe with external diameter 63 mm, thickness 4.5 mm, length 1 m, positioned horizontally; - filling with 10 cm of gravel (3 mm) to prevent the occlusion of the outlet fitting and having a filter function; - introduction of test soil in successive layers of about 20 cm, each of which was compacted by dropping a cylindrical steel mass (weighing 4 kg) into the tube, from a constant height of 50 cm; - closing of the pipe and its connection, through threaded ball valves, to the pump delivery pipe. The pump used in the laboratory is a single-component high pressure hydraulic system (220 ÷ 270 bar) with a maximum flow capacity of 6.5 l / min; - possible saturation of the ground; - mixing 2 kg of colloidal silica with water through a colloidal mixer (1800 rpm) for a period of 2 minutes; - injection of the mixture in the horizontal tube, at pressures Pi varying from 2 to 20 bar up to complete saturation of the specimen defined by the exit of the mixture from the final outlet connector of the experimental tube; - disconnection of the tube from the injection system and set aside for a time the function of the colloidal silica in question; Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

- connection of the hose to an air compressor (15 ÷ 20 bar) and expulsion of the treated soil into a special core drill bit. After 24 hours of rest, the samples are allowed to mature in water at a temperature of 20 ± 2 ° C before the mechanical tests at 2, 7 and 14 days.

Soil k (m/s)

Type “A” 1,18 E-04

Type “B” 9,50 E-06

Type “C” 5,30 E-05

Type “D” 2,20 E-05

Tab. 1 - Values of k of the soils subjected to laboratory "TEST"

Injection tests showed excellent penetrability in soils with injection pressures below 30 bar.

In injections of test soils the pressures that have been achieved are between 2 and 10 bar, and it has not identified any particular difficulties in completely permeate all available natural materials.

Mechanical monoaxial compression tests in the laboratory on incoherent injected soils.

The mechanical properties (strength and deformability) concern as initial reference data to define the consolidation requirements.

The tests were carried out according to the EN 12504-1 standard by means of an electrohydraulic press with a maximum applicable load of 50 MPa. To compare the monoaxial compressive strength values measured on the carrots (of cylindrical geometry), extracted from the injection pipe, with those determined on cubic specimens, it was decided to carry out crushing tests on carrots having a h/d ratio equal to 1 (as also suggested by the EN 12504-1 standard).

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Fig. 5 - Uniaxial compression resistance for injected media with colloidal silica.

The tests carried out with mixtures produced with colloidal silica, with a percentage of Accelerator-CSG-kat to 10%, has shown that it is necessary to use a percentage of accelerant from 20% to 26% to achieve a gelling time of between 60 min and 15 min.

Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

This field of application is justified by the compatibility of the use of colloidal silica with the traditional mixing and pumping systems used in normal construction applications. In fact, too low timing, could lead to the injection blocks due to gelation of the mixture and, consequently, to the non-success of the injection treatment and the loss of injection due to delays of construction operations.

All photos illustred are copied from the WEB

On the other hand, as regards the viscosity of the mixtures made with colloidal silica, laboratory tests have provided the classic evolution of the evolutionary mixtures. Finally, the injection tests showed the great penetration capacity of mixtures made with colloidal silica in all the types of soil used, even in those that had a high content of fine parts, with low injections pressures: tablets between 2 and 10 bar.

Therefore, by analyzing the results of the monoaxial compression tests, on the specimens of soils injected with colloidal silica in solution with the Accelerator-CSG-kat at 10% of NaCl, values between 0.2 and 1.2 MPa were obtained.

Fig. 6 - Penetrability of some mixtures as a function of the grain size and permeability of soils

However, without prejudice to the general properties of the injections with colloidal silicas, the optimal choice is a function of the objectives to be achieved based on the characteristics of the soil.

Permeability tests in rock I would like to point out that it is possible to perform permeability tests in rock both in the laboratory and in situ.

Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

As far as rocks are concerned, except for the case of porous structure or chemicalmineralogical peculiarities, laboratory investigations generally have little to say for the specific purposes of injectability.

However, the principle consists in measuring the water flow rates absorbed at different increasing and decreasing pressures, keeping constant each pressure value for 10 minutes.

The result is conventionally expressed in Lugeon Unit (U.L.), corresponding to the absorption in liters / min per meter of hole and with net pressure of 10 N/cm2.

In conclusion, the tests of water in fissured rock may give useful guidelines only if accompanied by geo-hydrological information, but from experiences on the latter test, generally initially occur of injection tests in situ, but only to define the more appropriate methods of treatment.

Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

ILLUSTRATIVE TECHNICAL REPORT PERMANENT SHOES, IMPROVEMENT AND REINFORCEMENT TECHNIQUES

The following Illustrative Technical Report is written as a variation/alternative to the << ... CONSOLIDATION OF DEGRADED ROCKET SHOES ... >> with Colloidal Silice present as an entry in the "fields of employment" in the previous report.

Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

In geological and geotechnical studies the relaxation of boulders along the detritic slope of the escarpments, known as "cortical failure", is one of the most studied phenomena of soils and rock masses, particularly in correspondence with the surfaces of discontinuity, because they involve instability processes. of the widespread phenomena of alteration.

The disruptions in the rock mass, usually, develop progressively over time and sometimes can put in crisis the global stability of entire surfaces, especially if these are mountain areas typical of our territory.

In fact, the rocky part characterized by congenital discontinuity or stratification joints is the one most subject to the action of atmospheric agents that accelerate its degradation such as the action of water (washout, encrustations, hydrostatic thrusts, ice, etc.) , of the wind and of the thermal excursions, together with the thermal expansion, the action of spreading the roots of the plants (wedge effect of the roots inside the fractures), and above all not to underestimate the karstic dissolution, the mineralogical alteration, and the hydration processes and argillification, a very important factor which causes instability over time. All this determines the priming in the rock mass of slow deformation phenomena which with unpredictable progression over time and with irreversibility character, lead to localized collapses with consequent collapse or fall of large rock volumes.

Generally the part of the rock mass involved in this phenomenon is the cortical thickness which usually does not exceed 1 - 2 m even if the degraded part can easily reach the depth of 5 - 10 m.

The analysis of core samples acts to highlight the fratturative characteristics together with a series of the mass rocky data (spacing of the fractures, geomechanical and humidity conditions, chemical and physical characteristics of the blanket and of its thickness, its inclination, the severity of situation, etc), put the specialists of the territory in the conditions to choose between a myriad of types and systems of facing the slope, with reclamation and / or consolidation systems that allow to increase the stabilizing forces and tend to improve the geotechnical characteristics of the same. Also they play a fundamental part of the anchorages system, which usually are chosen by geologists and engineers according to geometrical and geotechnical characteristics of the site on which they must intervene. (NTC of 2008)

Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

This article, wants to bring to your attention an improvement solution to the many known techniques for consolidation and / or cortical strengthening of slopes with relaxation phenomena in progress or landslide, using a "systematic association" of metal meshes and anchors (nailing or bolts) of the rocky face.

The function of metal nets and anchors (nailing or bolting) is to prevent the movements in the rock mass and to avoid the fall of stones or blocks for desquamation or splitting of the walls or for the sliding of rocky volumes.

In fact this "systematic association" has the task of transferring the stresses on the anchors and, through these, to the rock in depth. In particular, their function is to mitigate the risk due to the detachment of coulters of land and / or detrital material (collapses or landslides).

There are many difficulties encountered in securing the phenomenon of cortical failure because these interventions require, without any controversy, an increasingly specialized degree of preparation towards new technologies and new innovative products. In fact, the designers often have to solve big problems in very short times because of the urgency and danger of the situation, finding in short time an optimal solution that reduces the level of risk, the nature of the instability without altering the landscape appearance. The executing companies are also involved, with their executive limits of the operators on the wall and lastly the industries producing materials, such as metal nets, bars for nailing or anchors, the cements and resins of which there is still today it is a low degree of knowledge.

Starting from the state of the art, the first step is undoubtedly to begin to systematically investigate the intervention solutions related to geological problems and to identify the behavior of the materials to be used in advance, with adequate means and sufficient capacity for forecasting. To highlight the use of resins, as a consolidating and / or waterproof sealing system of fractures present in the cortical thickness of 1 - 2 m, capable of increasing the resistance to cutting along these directions, thus also easing the subsequent work of the anchors increasing the resistance of the rock mass to the Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

chemical-physical action of the percolation waters. In fact, the realization of such an impermeable and / or stabilizing barrier allows to increase the consolidating forces by improving the geotechnical characteristics of the whole rock mass, reducing the majority of the risk factors that could arise in the future.

Therefore, we can divide the consolidation systems into two macro families: The SURFACE type of consolidation systems are those which perform multiple functions in cortical reinforcement applications such as surface erosion control and revegetation of slopes. Part of this type of intervention is the "geocomposite" system consisting of a double twisted metal mesh coupled, in the production phase, with natural bioreti in coconut or metal geotextiles, or the three-dimensional polypropylene anti-erosion system incorporated in a network of high strength steel wire. Much has been said about this type of superficial consolidation and much literature has been produced on this subject.

The consolidation systems of the ACTIVE type: Used when there is an unstable thickness of rock up to about 2 m of depth, and consists essentially in the installation of anchorage bars (shear strength) perpendicular to the sliding surface, combined with a network in high-strength steel, thanks to which the system acts in a synergistic manner since the bars connected to each other thanks to the high mechanical resistance of the network.

The active stabilization system, as already mentioned, is one of the most recent technological innovations offered by the international market and is used for the combined protection against erosion, the fall of rocky debris, for the intervention on landslides, for deep instabilities and for securing slopes. Practically it is suitable for almost all types of slopes, whether solid or unstable rocky and covered with soil or other materials.

Below we will illustrate the elements used for the ACTIVE system for consolidation and / or strengthening of the cortical layer: Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

The metal meshes The networks applied on the rock walls are designed to control or prevent the development of cortical disruptions that occur with the detachment of boulders and distinguish two categories of protection networks: - simple protection networks generally fixed only at the top; - networks combined with a systematic nailing of the wall with a mesh of anchors aimed at more unstable cortical strengthening. In this case, a double-twisted network is preferably used which avoids the spread of damage inside the structure due to local breaks in the steel wires. The mesh wire can usually have different degrees of protection (strong galvanizing, eutectic alloy of ZN.AL, plastic polymers) depending on the durability requirements related to the application field. The tensile strength value of a wire mesh must be between 350-500 N / mm2 according to EN 10223-3 standards.

The bars for nailing or anchors The bars usually consist of active or passive point elements and are generally made of steel material with improved adhesion Ø 30 mm, self-piercing hollow bars, nails in B450C, steel strands usable as nails or piles or drill bits for all terrains and rocks.

Lately, the self-piercing bars have been used extensively, consisting of a variabledisplacement drill bit depending on the type of terrain. It is available on the market a wide range of variants able to support the last loads from 210 kN to 1,900 kN and which have all the related components: tips, sleeves, centering devices, heads and distribution plates to be used according to specific applications. The fields of application can be the most varied, but mainly are used for slopes, excavations, for fixing rockfall networks, barriers to avalanches and for foundations and slabs.

Cements Almost everything is known about cements today. As is known the main problem in the use of cement grout to block / anchor the bars for nailing or anchoring, is the withdrawal due to a volume variation caused, during the setting and hardening phase, by the progressive elimination of the water contained in it. This phenomenon is even more pronounced the faster the loss of water from the mass and causes the occurrence of cracks with consequent repercussion on the durability of the same.

Today, fluidifying and expanding additives are used to make fluid and anti-shrinkage grout for injection. The expansive effect allows to completely cancel the hydraulic shrinkage and to give the grout an expansion both in the plastic phase and in hardening.

The anti-shrinkage grout is able to guarantee greater durability even if, during the injection phase, unlike the resins, they tend to remain circumscribed to the drilling area of the anchor bar, penetrating with difficulty the interstices present in the fractured rock .

The use of resin injections in "cortical failure", especially used as a consolidating system in the thickness of 1 - 2 m of rock masses or at the same time as nailing or anchoring bars, are techniques to which the right importance is not given in Italy as it turns out to be abroad, especially in Asia, Australia, Canada, USA and South Africa.

Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

The deterioration of our environment requires more and more annual maintenance programs, only to maintain current levels of exercise. From an environmental and ecological point of view, today resins are also available that provide effective solutions in terms of durability much longer than other products and with very low maintenance costs.

The operative methodology of this type of intervention consists in injecting a chemical resin formulation able to penetrate also in the shale formations, thus increasing the cohesion of the ground, so as to avoid sagging, collapsing or falling of the front rocky volumes, and in particular way improving the mechanical strength of the rock mass.

Please note that the injectability depends mainly on the hydraulic characteristics of the rock mass, which are in turn influenced by the degree of fracturing, the characteristics of the discontinuity and the mechanical properties such as deformability and original stress state.

Unlike the grout, the resin injection formulation, as can be seen from the technical characteristics illustrated below, has particular properties that can guarantee good penetration in fractures, low viscosity, zero shrinkage, lack of run-off and good mechanical resistance to compression.

In fact, from our specific knowledge gained in the field we have found several times that the consolidation intervention carried out using the grout has a much lower durability than that performed with the resins due to the little expandability of the substance in the rock mass.

For this reason we suggest, for this type of problems, to intervene by means of a system of "injections" with the formulations of silicate resins directly into the slots in order to fill every gap in the rock, including pores and capillaries, and eliminate the infiltrations d ' water of any nature.

Operating in this way the first 2 meters of the rock mass thus treated becomes completely compact and cohesive with the homogeneous rock behind, impermeable even if the presence of water is of a negative hydrostatic nature.

Normally the operative methodology adopted to perform injections in the rock mass normally takes place, according to the following steps: - Realization of holes of diameter 13 mm, of variable depth from 3-5 cm, and with a three interval the holes of 30-50 cm.

- Installation of "packers" equipped with ball valves.

- Execution of injections made through special purpose pumps to variable parameters, with dosages which can vary at the volumetric ratio, also ensuring the steady flow in both flow rate and pressure.

An important precaution to be taken at this stage, for a performance made to perfection, is to not fill the cracks because, having an overview of the treated area, we are able to evaluate the "path" of the resin in the rock mass and therefore be able to Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

dose or even temporarily interrupt its flow. The injectability of the resin depends on the degree of cracking, on the discontinuity of the same, on the mechanical properties such as deformability and stress state of the rock mass.

The resinous injection mixture, as already mentioned previously and also detectable by the following technical characteristics described in the table, it must possess the conditions such as to ensure a good penetrability in the lesions, a low viscosity, a withdrawal and a washout absent and a good resistance compression. It must not contain fine particles so it can penetrate all the cracks and voids like water.

The formulation to be injected must be a resin (resin formulated) based on silicon-mineralorganic, of the bicomponent type, without expansion capacity, with high mechanical resistance and a high chemical stability and not polluting.

In fact, the resin we are proposing meets the above requirements and also responds to the Test Reports of the "ASSESSMENT TESTS" (UNI EN 12457-2 Method) for the use and use of the resin in the presence of groundwater according to the D.Lgs. n. 152/06 P.IV-TV- All. 5 Tab and the "CESSIONE TEST" for the use and use of the resin in the presence of water for human use according to the D.Lgs. No. 31/01. This type of product has been studied and developed specifically to solve the type of problem addressed in this article. In fact, the reaction of the formulation is irreversible and the mixing between the two components "A" and "B" takes place in very short times (1 - 2 minutes at + 18 ° C.). In the presence of particular work situations or in adverse climatic conditions, this chemical reaction can be modified by adding an accelerating additive in the order of 0.5 - 1% in the "A" component. Moreover, the presence of water, diluent par excellence, during the injections operations does not influence in any way neither the chemical reaction nor the expandability of the product being the latter mainly of an inorganic nature.

Analyzing the coring performed at the end of the work to verify the correct execution of the intervention, it will be noted that the material has an elasticity and excellent adhesion to the various types of material constituting the rock mass. This formulation is also selfextinguishing.

We conclude by quoting a sentence taken from the geotechnical legislation that states: "The value of the safety coefficient will be assumed by the designer and justified on the basis of the considerations of the level of knowledge achieved and the degree of reliability of the available data, the complexity of the geological and geotechnical situation. , to the local experience on natural slopes in similar situations, as well as to the consequence of a landslide ".

Therefore, we would like to underline that in the planning stage, being aware of the greatest possible data, including the compatibility requirements of the various materials and the different durability of the elements, is not to be neglected with the ultimate goal of achieving a best possible safety coefficient.

Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

Caratteristiche chimico-fisiche della “resina” Natura chimica componente A

silicati inorganici in soluzione acquosa, amminoalcoli

Applicazione

difenilmetan 4,4 diisocianato, prevalentemente polimerico, più additivi siliconici e additivi antifiamma.

1.450 ± 0.05 Kg/dm3 1.180 ± 0.05 Kg/dm3 300 - 600 mPas. 550 - 750 mPas. 11.5 ± 0.5 Neutro 100 + 100 parti in volume/ 100 + 83 parti peso mediante iniezione, usando apposite pompe con miscelatore statico, con pressione sino a 100 atm.

Inizio della reazione Reazione completa Esotermia di reazione Resistenza a compressione Resistenza a flessione

1 - 2 minuti dopo 5 – 10 minuti max 90 – 100° C 18 - 21 N/mm2 5.50 – 6.18 N/mm2

Natura chimica componente B Peso specifico componente A Peso specifico componente B Viscosità componente A Viscosità componente B pH componente A pH componente B Rapporto di miscelazione

Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

At the end of these nr. 2 brief reports I add some photos illustrating the waterproofing and consolidation work scheme with "colloidal silica" and "organo-mineral" resin

Foto 1

Foto 2

Photos 1, 2 and 3 illustrate how a watercourse was regimented by injection of Silica Collaida, stone walls and "corten" tubes.

Foto 3

Foto 5

Foto 4

Foto 6

Foto 7

The photos 4, 5, 6 and 7 illustrate the stabilization of a rocky ridge with nailing and harnessing the boulders in the wall by filling the cavities with an organo-mineral silicate resin. In all, 13 deep probes of up to 80 meters were carried out, most of which consisted of continuous drilling, from which structural indications and the stratigraphic sequence of the soils were obtained.

In the surveys the low RQD value (20 - 25%) and the existence of brecciated levels even of high thickness (max 22 m) were remarked. it was decided to also perform an accurate survey geomechanical, using, for relief operations in the wall, otherwise executables, skilled climbers.

Before any intervention, an accurate removal of the boulders on the wall was carried out in order to eliminate the immediate dangers for the personnel in charge of resin injections and the inhabited area below.

All photos illustred are copied from the WEB

Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

All photos illustred are copied from the WEB

All photos illustred are copied from the WEB

Foto 8

Foto 9

The photos 8 and 9 illustrate the drawing of a typical example of the perforations of the holes for the injection of "Colloidal Silica" in a hydroelectric plant, under renovation, to obtain the consolidation of the ground in the less deep areas of the tunnels and for the contrast blocks of the pipelines. During the experimentation phase in situ, very large diameters have been planned in order to obtain the "columnar" treatment. In this case a double injection was foreseen in order to reach the resistances foreseen for the various treated areas.

Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

Bibliography

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AFTES (Association francaise des tunnels et de l’espace souterrain), Travaux d’injection pour Ouvrages Souterrains, in Recommandations de l’AFTES, n. GT8R1F2.

Akbut, S. e Saglamer, A. 2002, Estimating the groutability of granular soils a new approach, in Tunnelling and Underground Space Technology, n. 17.

ASTM C136 - 06, 2006. Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates.

ASTM D2434-68, 2006. Standard Test Method for Permeability of Granular Soils (Constant Head).

Axelsson, M., 2006. Mechanical tests on a new non-cementitious grout, silica sol: a laboratory study of the material characteristics in Tunnelling and Underground Space Technology, n° 21.

Bahadur, A.K., Holter, K.G. e Pengelly, A., 2007. Cost-effective pre-injection with rapid hardening microcement and colloidal silica for water ingress reduction and stabilisation of adverse conditions in a headrace tunnel, in Underground Space – the 4th Dimension of Metropolises, Taylor & Francis Group, London, Bezuijen.

Butrón, C., Gustafson, G. e Axelsson, M., 2009. Silica sol for rock grouting: Laboratory testing of strength, fracture behaviour and hydraulic conductivity, in Journal homepage, Tunnelling and Underground Space Technology, n° 24.

Cambefort, H., 1967. Injection des sols, Paris, Éditions Eyrolles.

Cambefort, H., 1977. The principles and applications of grouting, in Q. J1 Engng Geol., Vol. 10.

Chieregato, A., Oñate Salazar, C.G., Torado, C. e Peila, D, 2014. Mechanical improving of granular soils by permeation grounting: results of laboratory tests, in World Tunnel Congress.

Garshol, K.F., 2010. Rock Tunnelling with Groundwater Ingress Control - “Dry” tunnels using Pre Excavation Grouting, in ICE Breakfast Forum.

Holter, K.G. e Hognestad, H.O., 2010. Advantages in preinjection grouting, in Tunnels & Tunnelling International, Ottobre 2010, London, World Market Intelligence.

Holter, K.G. e Hognestad, H.O., 2012. Modern pre-injection in underground construction with rapid setting microcements and colloidal silica, in Geomechanics and Tunnelling, vol. 5.

Holter, K.G. Modern pre-injections in underground construction with microcements and liquid colloidal silica for water ingress reduction and ground improvement, in Geomechanics and Tunnelling, Karol, R.H., 2003. Chemical grouting and soil stabilization, New York, Marcel Dekker, Inc. Kolymbas, D., 2005. Tunelling and Tunnel Mechanics. A Rational Approach to Tunnelling, Berlin, Springer-Verlag Berlin Heidelberg.

Mahrholz, A. T., Stängle, J. e Sinapius, M., 2009. Quantitation of the reinforcement effect of silica nanoparticles in epoxy resins used in liquid composite moulding processes, in Journal homepage, parte A, n° 40.

Melbye, T., Hognestad, H.O. e Dimmock, R., Pre-Injection technology for mines, in 8th International Congress on Mine Water & the Environment, Johannesburg, South Africa Moseley, M.P. e Kirsch, K., 2005. Ground improvement, Taylor & Francis e-Library.

Mutman, U. e Kavak, A., 2011. Improvement of granular soils by low pressure grouting, in International Journal of the Physical Sciences, Vol. 6.

Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

Peila, D., Chieregato, A., Picchio, A. e Borio, L., 2010. Studio della permeabilità di terreni condizionati con schiume, in GEAM, Vol. XLVII, n° 2, Pàtron Editore.

Tornaghi, R., Bosco, B. e De Paoli, B., 2003. Application of recently developed grouting procedures for tunneling in the Milan urban area. 5th International Symposium on Tunnelling, London.

UNI EN 11152:05, 2005. Sospensioni acquose per iniezioni a base di leganti idraulici - Caratteristiche e metodi di prova.

UNI EN 196-3:05, 2005. Metodi di prova dei cementi - Parte 3: Determinazione del tempo di presa e della stabilità.

UNI EN 12504-1:09, 2009. Prove sul calcestruzzo nelle strutture - Parte 1: Carote - Prelievo, esame e prova di compressione.

Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.

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Lamanna Luigi Franco Independent Technical Consultant of the DPT Tunneling, Mining and Engineering

Thanks to the experience gained in the construction sector, in particular in Tunneling, Mining and Engineering, and to the most modern chemical technologies, it is able to offer solutions through specific technical consultancy ranging from specialist-application collaboration on site, to design support, in synergy with the staff of its customers and with the staff selected on site, to solve all problems by evaluating the best solutions.